Control of electronically generated light pulses

ABSTRACT

Circuits and auxiliary elements for use with a device for controlling the emission of light pulses from a flash unit, which light pulses are produced by the discharge of current pulses from a capacitor, the device including a light sensing element for receiving light produced by the flash unit and reflected from an object in the light path. One such element is constituted by light transmitting lens means having two distinct angles of acceptance extending in the same general direction and transmitting light to one or more light sensing elements. One such circuit includes two zener diodes for providing threshold voltages for use in comparing the output of the light sensing element. Another such circuit compensates for nonlinearities in the response of certain components of the device. Another such element is a special gas filled tube having an internal electrode for triggering conduction through the tube in response to a low voltage. One further element is a special gas filled tube having no internal electrode and constructed to be triggered by receipt of a light emission.

United States Patent [1 1 Vital et al.

[451 July 31,1973

[ CONTROL OF ELECTRONIC/ALLY 3,315,082 4/1967 Milroy 250/227 GENERATEDLIGHT PULSES 3,463,927 8/1969 Allington 250/227 X [75] Inventors: 3 g g'F g k orban Primary Examiner-Archie R. Borchelt I a o o eAttorney-Spencer & Kaye [73] Assignee: Ponder & Best, Inc., Los Angeles,

Calif. [57] ABSTRACT [22] Filed: M r, 9, 1970 Circuits and auxiliaryelements for use with a device for I controlling the emission of lightpulses from a flash film] Appl' 17634 unit, which light pulses areproduced by the discharge Related U.S. Ap li ti D t of current pulsesfrom a capacitor thedevice including 63 C t f S N 799554 F 13 a lightsensing element for receiving light produced by I gg' i x fgig 0 er 0 ethe flash unit and reflected from an object in the light path. One suchelement is constituted by light transmit- [30] Foreign Applicationpriority Data ting lens means having twodistinct angles ot' accep- M a r7 969 B el ium 71104 tance extending in the same general direction and gtransmitting light to one or more light sensing elements. [52] U 8 Cl250/214 P 250/227 250/229 One such circuit includes two zener diodes forprovid- [51] 6 39/12 ing threshold voltages for use in comparing theoutput I 5 Fie'ld 214 P of the light sensing element. Another suchcircuit compensates for nonlinearities in the response of certaincomponents of the device. Another such element is a [56] ReferencesCited special gas filled tube having an internal electrode for UNITEDSTATES PATENTS triggering conduction through the tube in response to3,350,604 lO/l967 Erickson 250/2 l4 P a low voltage one further elementis a pecial gas 3,600,584 8/197] Schneble 250/214 P tube having nointernal dectrode and constructed to be 2m: 2/1211 2:222:11: 2 24322: by3 l85,852 5/1965 Lewis 250/227 10 Claims, 35 Drawing Figures VOLTMETERI08 LIGHT SENSOR INTEGRATING m3 CIRCUIT BJECT I ESWITCH 1 I I05 FIRING l7 7 VOLTAGE CIRCUIT} l SUPPLY- I02 ,0 I00 705 i PATENIEU JUL3 1 I973SHEET 03 nr 10 Fig. 4

COMPENSATING DEVICE CAMERA SVNCHRONIZING CONTETS F ig.5

APERTURE INVENTORS Zolton Vital BY Jean Orbon ATTORNEYS.

PATENTEDJULB 1 3. 749.921

SHEET 03 0F 10 INVENTORS Zolmn Vital PATENIED 1 3.749.921

saw our 10 INVENTORS Zohun Vital y Jean Orbon %mew,

ATTORNEY PATENTEB JUL 3 1 I973 SHEET us or z r 0 w T O 0 R C 2 U L DO.m. T W F I dm ruw W m U C l'.

G N M W EU w m C C m 0.. n F RIITQ mm 1: W m 1 lllllll ll M u L D0FIIIIIIIIIA T m C f ATTORNEYS.

QZQQ.

INVENTORS Zolrun Vital Jean Orbon CIRCUIT COMBTNING Fig. 22

JJQJ LIGHT DURATIION Fig. 24

CONTROL CIRCUIT LIGHT DURATION CONTROL CIRCUIT LIGHT DURATION Fig. 27

LQQQI LIGHT DURATION CONTROL cmcurr IIIIIIFTIIB CONTROL CIRCUIT PATENTEDJUL3 1 I973 sum 07 nr1o FIG.25

ATTORNEYS.

PATENIEDJUL3 1 I915 3'. 749 921 SHEET 08 0F 10 FIG -28 FIG. .30

INVHVTORS Zolron Vircl BY dean Orbun we, I

AT TORNEYS.

PATENIEDJULB I I973 3 749,921

SHEET 09 0F 10 FIG. 31

FIG. 32

INVENTORS Zolton Vifol BY Jean Orbon ATTORNEYS.

CONTROL OF ELECTRONICALLY GENERATED LIGHT PULSES CROSS-REFERENCE OFRELATED APPLICATION BACKGROUND OF THE INVENTION The invention concernsadditional novel elements and circuits for use with the devices diclosedin our copending application Ser. No. 799,554, filed Feb. 13, 1969. Thatapplication discloses various devices for controlling the impulsesgenerated by the discharge of a capacitor placed either in series or inparallel with a load and, in the case of a parallel connection, havingno more than one electronic switch. The pending application alsodiscloses novel switching tubes for uses as such switch.

In known devices of the type here under consideration, reflected lightis measured by a light receiver having only one angle of acceptance andprovided with but a single light sensitive element.

One drawback of such devices is that when a high contrast scene, orsubject, is to be photographed, the reflected light will not be measuredwith sufficient accuracy. Moreover, when a reflected light measuring andduration control device is used in a camera, and the subject to bephotographed is moving and/or the illumination intensity is fluctuating,accurate measurement of the light reflected to the camera with knownlight measuring devices becomes difficult, and sometimes evenpractically impossible, and in any case requires a number of complexmeasurements, computations and evaluations.

SUMMARY OF THE INVENTION An object of the present invention is toprovide an improved measurement, computation and control of the lightproduced by a flash unit.

One specific object of the present invention is to provide a device forsimultaneously measuring reflected light with at least two differentangles of acceptance, which device may be provided with one or aplurality of light-sensitive elements. This device is suited forelectronic flash instruments, stroboscopes, lasers etc., which arepreferably provided with an automatic flash duration control, as well asfor still cameras, movie cameras, photographic enlargers, light meters,etc. This method intends to produce a better evaluation, computation anddosaging of the reflected light.

For this purpose, the present invention provides a light metering devicewhich has at least two different angles of acceptance, preferably havingdifferent sensitivities with or without light conductors and providedwith one or a plurality of light receivers, which may be constituted byphotodiodes, phototransistors, photoresistors, sun batteries, etc.

When such a device is used in a photographic electronic flashinstrument, a stroboscope or laser, etc., each measurement made duringthe flash duration is transferred, before or after integration, to acomputing circuit, performing, for example, addition, subtraction,division, or multiplication operations, or combinations thereof, whichproduces the control signal to be transmitted to the flash durationcontrol device.

When such a device is employed in a still camera, a movie camera, etc.,the control signal is instead transferred to these devices.

Another object of the present invention is a control device forpulseswhich are produced by the discharge from a capacitor, and whichare delivered, for example, to the flash tube of anelectronic flashunit. The control device employs two zener diodes as threshold valuedetectors and which is also provided with a circuit which compensatesthe time delay of certain components and the fluctuations in thezener'voltage of the zener diodes, thereby to permit the flash unit tobe controlled at different light intensity settings. This device issupplemented by a photoelectronic remote triggering device provided witha system which permits use even with indirect flashes from the flashunit. Means are provided to permit automatic switching between thedevices.

Any of the light control devices described in our copending US.application Ser. No. 799,554 may be supplemented with a threshold valuedetector consisting of two zener diodes, a resistor for the compensationof the delays and variations in certain components, and a switch whichpermits operation of the light control device with a full lightintensity output or a partial light intensity output of the flash unit.

A further object of the present invention is a device for controllingthe pulses generated during the discharge of a capacitor and employing agas-filled switching tube whose interior is provided with one or aplurality of triggering electrodes, which are designed to operate atrelatively low voltages, preferably between 50 and 1,000 volts, whencompared to similar known devices or is provided with an electricallyresponsive light generating device which permits the use of a gas-filledtube having only the two main electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramof a basic cir cuit with which the improvements according to the presentinvention can be used.

FIG. 2 is a schematic circuit diagram of another form of construction ofthe circuit of FIG. 1.

FIG. 3 is a more detailed circuit diagram containing a more detailedshowing of one embodiment of a flash duration control circuit.

FIG. 4 is a view similar to that of FIG. 3 of another embodiment of aflash duration control circuit.

FIG. 5 is a view similar to that of FIG. 3 of still another embodimentof a flash duration control circuit.

FIG. 6 is a view similar to that of FIG. 3 of yet another form ofconstruction of a flash duration control circuit.

FIG. 7 is a view similar to that of FIG. 3 of a further form ofconstruction of a flash duration control circuit.

FIG. 8 is a view similar to that of FIG. 3 of yet a further embodimentof a flash duration control circuit.

FIG. 9 is a view similar to that of FIG. 3 of a still further embodimentof a flash duration control circuit.

FIG. 10 is a view similar to that of FIG. 3 of an additional embodimentof a flash duration control circuit.

FIG. 11 is a view similar to that of FIG. 3 of a further additionalflash duration control circuit.

FIG. 12 is a view similar to that of FIG. 3 of another additionalembodiment of a flash duration control circuit.

FIG. 13 is a pictorial view of one embodiment of a dual field lightreceiver according to the invention.

FIG. 14 is a view similar to that of FIG. 13 of another embodiment ofthe light receiver.

FIG. 15 is a view similar to that of FIG. 13 of a further embodiment ofthe light receiver.

FIG. 16 is a view similar to that of FIG. 13 of yet another embodimentof the light receiver.

FIG. 17 is a view similar to that of FIG. 13 of still another embodimentof the light receiver.

FIG. 18 is a view similar to that of FIG. 13 of still a furtherembodiment of the light receiver.

FIG. 19 is a circuit diagram ofa light sensor arrangement according tothe present invention.

FIG. 20 is a view similar to that of FIG. 19 of another light sensorarrangement.

FIG. 21 is a view similar to that of FIG. 19 of still another lightsensor arrangement.

FIG. 22 is a view similar to that of FIG. 19 of a further sensorarrangement.

FIG. 23 is a view similar to that of FIG. 19 of yet a further sensorarrangement.

FIG. 24 is a view similar to that of FIG. 19 of a still further sensorarrangement.

FIG. 25 is a circuit diagram of a modified light duration controlcircuit according to the invention.

FIG. 26 is a circuit diagram of a control circuit according to theinvention for controlling both the initiation and termination of a lightflash.

FIG. 27 is a perspective view of an automatically controlled flash unitaccording to the invention which can contain the circuit of FIG. 26.

FIG. 28 is a circuit diagram of a control circuit according to theinvention employing a low voltage activated gas-filled tube.

FIG. 29 is a view similar to that of FIG. 28 of another embodiment ofsuch circuit.

FIG. 30 is a view similar to that of FIG. 28 of a further embodiment ofsuch circuit.

FIG. 31 is a view similar to that of FIG. 28 of a further embodiment ofsuch circuit.

FIG. 32 is a view similar to that of FIG. 28 of a still furtherembodiment of such circuit.

FIG. 33 is a view similar to that of FIG. 28 of yet another embodimentof such circuit.

FIG. 34 is an elevational view of one embodiment of the gas-filled tubeemployed in the embodiments of FIGS. 28-31.

FIG. 34a is a cross-sectional view of a modified form of construction ofthe embodiment of FIG. 34.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I shows the circuit of anelectronic photoflash equipped with a control device having only oneswitch whose purpose is to arrest the capacitor discharge when apredetermined amount of light has been produced.

The arrangement of such a unit is as follows.

An energy storage capacitor 100 is charged through a voltage source 101.A flash tube 102 of the usual type is connected to the capacitorterminals through a switch 103 which is preferably a gate-turn-outthyristor or thyratron, etc., provided, if necessary, with suitablesupplementary circuitry. A light sensor 104, composed of a photodiode,phototransistor, photoresistance, or other, is connected to anintegrating circuit 105 of any well-known type. A firing circuit 106triggers the firing of the flash tube 102. This device works as follows.

The capacitor having been charged by the source 101, the ionization ofthe flash tube 102 is induced by the action of the firing circuit 106.The light sensor 104 supplying an instantaneous current proportional tothe illumination on subject 107, to the integrating circuit 105, thelatter, when the total amount of light received by the light sensor 104reaches a predetermined value, causes a circuit to swing", thussupplying an impulse to the switch 103 which then interrupts thedischarge of the capacitor 100.

Thus, the light emission of the flash tube is arrested after producingthe requisite amount of light, without any energy being withdrawn fromthe capacitor other than that used for producing the light, and possiblyfor commutating the circuit.

The arrangement of FIG. 1 may be completed in the following manner: byconnecting a voltmeter 108 to the terminals of the integrator circuit105, which is designed for such a connection, an integrating photometer,or chronometer, can be produced, which device has scales in differentmeasuring units.

Another variant is illustrated in FIG. 2 in which we describe a controldevice connected both in series and parallel with the load and combinedwith a compensating device, capable of also being used with thepreceding embodiment, constituted by an induction coil.

The discharge capacitor 200 is charged through the voltage source 201.The flash tube 202 is connected to the terminals of the capacitor 200through the intermediary of the induction coil 203. A thyratron 204 isconnected in parallel with the flash tube 202. A light sensor 205 iscoupled to the integrating circuit 206, receives reflected light fromsubject 209 and controls the firing electrode 207 of the thyratron 204.A firing circuit 208 acts to fire the flash tube 202. Meter 210 isconnected to circuit 206.

The operation of the circuit of FIG. 2 differs from that of FIG. 1 asfollows.

After reaching the predetermined signal value, the circuit of theintegrator 206 triggers the firing electrode 207 of the thyratron 204 inparallel with the flash tube 202. The induction coil 203 allows for ashort period during which the thyratron is practically in shortcircuit.Consequently, the flash tube 202 has enough time to deionize, and henceto become extinguished.

A modification is illustrated in FIG. 3. This control device is combinedwith both an electronic gate and an optical device of regulation of thesensitivity.

The control device consists of an electronic device 30 which isidentical with the device 50 of FIG. 5, of the photoflash unit 31 and ofan electronic switch 32.

In this device, a light sensor 301 generates a current proportional tothe relfected light from the subject. This current is integrated by acapacitor 302 to give a voltage proportional to the amount of thereflected light. This voltage is applied to a unijunction transistor 304or to a four-layer diode or to some other element or device which wouldserve as suitable substitute, which develops a positive impulse in theresistance 305 as soon as the threshold swing or switching level, ofthis component 304 has been reached.

This impulse is conducted by the capacitor 306 to open a semiconductorswitch, or other element, 308 by means of its firing circuit whichcontrols the electronic switch 32 so as to terminate the capacitordischarge and thereby extinguish the flash tube of the photoflash 31.

As soon as the cycle is'ended, the voltage across a resistance 303 setsthe system back to its initial condition. A resistance 307 prevents apremature opening of the semiconductor switch 308. The unit 31 containsthe elements of the photoflash which are not individually referenced.The electronic device 30 contains as its principal element asemiconductor switch, such as a thyristor (SCR), or else a gas-filledswitching tube, preferably of the arc arrester type or a special arcarrester, or another suitable component.

An improvement of the flash control device consists in equipping thisdevice with an electronic gate which acts upon the reflected lightsensor circuit.

FIG. 3 also illustrates the electronic gate arrangement. When the flashtube is fired, the voltage at the flash tube terminals decreasessharply. This results in a current in the circuit of the capacitor 309,the resistance 310 and the zener diode 311. A voltage equal to thatacross the zener diode is to appear at the terminals of the light sensorcircuit so as to place it in operation. The current intensity depends onthe resistance value of resistor 310. The opening duration of theelectronic gate of the light sensor circuit depends on the value of thecapacitor 309.

The regulation of the sensitivity of the control device is effected bythe user with the help of an adjustable optical device 315 composed of adiaphragm, aset of filters, or others, placed-in front of the lightsensor 301 of the control device.

A further explanation is given with reference to FIG. 4 which shows alight control device for the flash of an electronic photoflash,consisting of the electronic device 40, which is similar to the device30 of FIG. 3 and the device 50 of FIG. 5 and which is therefore onlypartially shown, of the photoflash 41, which is similar to the device31, and of an electronic switch 42, which is similar to the device 32,connected in series with the flash tube circuit.

This device and its operation are essentially identical to thosedescribed and illustrated previously, namely:

The thyristor 421, which is fired upon closing of the camerasynchronization contacts, applies the voltage of the discharge capacitor411 across the flash tube 412, the latter having received previously afraction of this voltage, the value of which fraction is determined bythe resistances 404 and 423, and to the tube firing circuit consistingof a capacitor 413 and a transformer 414, thus firing the flash. Whenthe thyristor 401 becomes conductive due to the subject having beensufficiently illuminated, it discharges the capacitor 402, which waspreviously charged, into the thyristor 421, which results in reversingthe anode voltage of the thyristor for a short period so as to cause itto block and thus arrest the discharge of the capacitor 411. Thecapacitance value of the capacitor 402 is selected so as to obtain animpulse of sufficient duration to allow the extinction, or blocking, ofthe thyristor 421. The capacitance value of the capacitor 422 isselected so as to obtain the shortest possible impulse so that theextinction of the thyristor 421 may occur as rapidly as possible. Theresistances 424 and 425 are used to polarize the capacitor 422. Thevalue of resistance 403 must be selected in order to give a currentlower than the maintenance current of the thyristor 401 so as to preventthe capacitor 411 from continuing to discharge itself through thethyristor 401. A compensation device, such as an induction coil, 415modifies the discharge impulse in the flash tube. Among other things, itlengthens the discharge duration, etc.

FIG. 5 shows a control device combined with an electronic gate and withan optical device for the regulation of sensitivity. This control deviceconsists of an electronic device '50 and the photoflash 51.

The components and operation of this device are identical to thosedescribed with reference to FIG. 3, with the difference that an impulsetransmitted by the capacitor 506 opens a semiconductor switch, or aspecial arc arrester, etc., 508, via its firing circuit and therebyextinguishes the flash tube 512 of the photoflash while discharging thecapacitor 513 of the latter.

In FIG. 6, we describe another embodiment equipped with a special arcarrester combined with an electronic gate and with an electric devicehaving several capacitors for the regulation of sensitivity. A specialarc arrester 611 and its firing device, which consists of the thyristor606, the resistances 607 and 608, the capacitor 609 and the transformer610, serve as a substitute for the thyristor 508 of FIG. 5. Here, wemake use of an electric circuit for adjusting the sensitivity, thecircuit consisting of a switch 615 connected to select one of thecapacitors 603 and 604 having different capacitance values.

In FIG. 7 there is shown another embodiment in which the photodiode isreplaced by a phototransistor 702 in order to give a higher sensitivityto the light integrator than is possible with the photodiode. In FIG. 8the photodiode 802 has an amplification circuit composed essentially ofan npn transistor 803 which allows the selection of a very highsensitivity, as a function of the gain of the transistor.

In FIG. 9 a pnp transistor 903 replaces the npn transistor.

In FIG. 10 the light sensor is a photovoltaic cell, such as a solarcell, etc., 1002, the current of which is amplified by a transistor1003.

In FIG. 11 the firing of the thyristor 1106 is effected by a thresholdamplifier which consists of the transistor 1114 and the resistances1103, 1105, 1115 and 1116. The switching threshold may be adjusted orregulated internally and/or externally by means of the resistance 1103.The threshold voltage determines the control device sensitivity.

In FIG. 12 the threshold amplifier contains two transistors 1214 and1216. The switching threshold may be adjusted by selecting suitablevalues for the resistances 1215 and 1203.

FIGS. l-12 are disclosed in our copending parent application.

There will now be described various embodiments of the presentinvention.

FIG. 13 shows a light sensor 2201 which is provided with two ancillarylenses, or lens systems, 2202 and 2203 having respectively differentangles of acceptance, as illustrated, for light traveling in thedirection of the arrows. The light gathered by each lens is conveyed,still in the form of light, to light-sensitive element 2201 where it isconverted into electrical signals in a well-known manner.

FIG. 14 shows a light-sensitive element 2301 with one ancillary lens orlens system 2302 having three different focal lengths, or angles ofacceptance.

FIG. shows a light-sensitive element 2401 which is disposed behind twolight conductors 2402 and 2403, which may be constituted by opticalfibers, transparent material, etc. Lenses 2406 and 2407, possibly havingrespectively different light attenuation characteristics and in any casehaving respectively different angles of acceptance 2404 and 2405 areplaced in front of the light conductors.

FIG. 16 shows substantially the same arrangement as FIG. 15, except thatonly one light conductor 2502 is employed, a bifocal lens 2506 beingplaced thereinfront and having two portions 2507 and 2508 withrespectively different radii of curvature and angles of acceptance, andpossibly respectively different optical attenuation characteristics.

FIG. 17 shows a device with two light-sensitive elements 2601 and 2602provided with respective lenses 2603 and 2604 having respectivelydifferent diameters and angles of acceptance.

FIG. 18 shows an arrangement similar to that of FIG. 17 but with twolight-sensitive elements 2701 and 2702 having the same angle ofacceptance disposed behind an optical device consisting of two lenses2705 and 2706 with respectively different angles of acceptance 2703 and2704 and two light conductors 2707 and 2708.

FIG. 19 shows one embodiment of a combining circuit 2803 whichalgebraically adds the two partial currents from the twoparallel-connected light-sensitive elements 2801 and 2802, here shown astwo photodiodes. The circuit 2804 contains the remaining circuitelements. The two photodiodes are arranged to each receive light from arespective one of the two lenses of FIGS. 13, 15, 17 or 18, or from arespective portion of the composite lenses of FIGS. 14 and 16.

FIG. 20 shows substantially the same arrangement as FIG. 19, but the twolight-sensitive elements 2901 and 2902 are photoresistors which, in theembodiment of an electronic flash unit also themselves perform the lightintegration operation and are followed by a light duration controlcircuit 2903.

The resistance of each photoresistor corresponds during the duration ofaflash to the amount of light received at each instant.

FIG. 21 corresponds essentially to FIG. 20 except that the twophotoresistors 3001 and 3002 are connected in series with controlcircuit 3003.

FIG. 22 is similar to FIG. 21, except that the signal of one ofthe twophotoresistors 3101 is additionally fed to a separate input of thecomputing circuit 3103. The circuit 3104 contains the other elements.

FIG. 23 corresponds substantially to FIG. 19, except that the combiningcircuit contains a voltage divider which consists of potentiometers 3203and 3204 and fixed resistors 3205 and 3206, having their common junctionconnected to control circuit'3207. Thus, the effective sensitivity ofthe two light-sensitive elements 3201 and 3202 can be separatelyregulated.

FIG. 24 shows an automatic light duration control device which isprovided with two light-sensitive elements 3301 and 3302. Eachlight-sensitive element has its own integration circuit which consistsof a respective one of the capacitors 3303 and 3304. The capacitorvoltages are applied to respective ones of the two voltage dividerswhich are formed of the variable resistors 3305 and 3306 and the fixedresistor 3307. The

two voltage dividers have a common output terminal connected to controlcircuit 3308.

The voltage of the fixed resistor 3307 is applied to a threshold valueamplifier which is disposed in circuit 3308 together with the otherelements of the light duration control device.

The arrangements illustrated in FIGS. 19-24 can be substituted for thelight-sensitive element assemblies of the circuits of FIGS. 1-12. Forexample, the elements 2801, 2802 and 2803 of FIG. 19 or the elements3001 and 3002 of FIG. 21 could simply be plugged in in place of thelight sensor of any of the circuits of FIGS. 1-12. The embodiment ofFIG. 23 could be connected in the circuit of FIG. 11 by removing thelight sensor of the latter figure, connecting terminal 3210 of FIG. 23to the upper power supply conductor of FIG. 11, connecting FIG. 23terminal 3211 to the capacitor shown in FIG. 11 to be connected inseries with the light sensor, and connecting FIG. 23 terminal 3212 tothe emitter of amplifier transistor 1114 of FIG. 11. The embodiment ofFIG. 24 could be connected in the circuit of FIG. 11 in a similarmanner, but in this case both the light sensor and its seriesintegrating capacitor of FIG. 11 would be removed. The embodiments ofFIGS. 23 and 24 could similarly be incorporated in the circuits of FIGS.1-10 and 12.

FIG. 25 illustrates one embodiment of a circuit possessing other novelfeatures according to the invention. In this case two zener diodes 3401and 3402 are employed in a series connection so that the total voltageacross them determines the supply voltage of the lightsensingphototransistor 3403. The voltage across the zener diode 3402 alonedetermines the value which the voltage across the integration capacitor3404 must reach in order to fire the thyristor 3405.

The circuit includes a resistor 3406 across which is produced a voltageproportional to the nonlinearity error of the control device, whicherror is caused by voltage fluctuations of the zener diodes 3401 and3402, by the switching delays of the thyristor 3405 and by the arcarrester 3407. The resistor 3406 is connected in such a way as tocompensate this error.

When thyristor 3405 fires, i.e., becomes conductive, it causes capacitor3412 to discharge through the primary winding of a transformer 3413whose secondary winding is connected to arrestor 3407. The voltage towhich capacitor 3412 is charged prior to the firing of thyristor 3405 isdetermined in part by the value of resistors 3409, 3410 and 3411.

A switch 3408 is connected across resistor 3409 and when this switch isopened resistors 3409, 3410 and 3411 determine the voltage of the firingcapacitor 3412, corresponding to the full power output of the flash.

When switch 3408 is closed, only the resistors 3410 and 3411 determinethe voltage of the firing capacitor corresponding to a partial poweroutput from the flash.

According to another feature of the invention, the light control deviceof an electronic flash unit can be supplemented to give it thecapability of initialling functioning as a light responsive flashtrigger device, or slave unit, and then automatically switching tofunction as a light duration control unit. This combined device is soconstructed that it performs the automatic switching between the twomodes of operation. This device preferably employs a singlelight-sensitive element to initiate the two functions, and possiblyfurther common components. This means that during its periods of use asa remote triggering device, the light-sensitive element is notconducting an electric current and thus operates as a simplephotovolltaic element or the like, whereas during the period when itoperates as a flash control device, the light-sensitive element isconnected to an electric current supply and thus operates as aphotodiode or the like.

FIG. 26 illustrates one exemplary embodiment of such a device in whichthe circuit substantially illustrated in FIG. 6 is supplemented with thefollowing components:

a switch 3501 for connecting or disconnecting the remote triggeringdevice and a capacitor 3502 connected in series between thelight-sensitive element 3508 and the gate electrode of a thyristor 3503,as well as other components present in a conventional electronic flashassembly, such as the firing transformer 3504, the firing capacitor3505, the resistor 3506 and the flash tube 3507, thyristor 3503 beingconnected across the series arrangement of capacitor 3505 andtransformer 3504.

The device operates as follows.

When switch 3501 of the light duration control device of the flash unitis closed, the photoelectric remote triggering device is also renderedoperative. The lightsensitive element operates in this case principallyas a photoelement without any steady-state electric current.

In this mode of operation, when the light from an external main flashinstrument reaches the photoelement 3508 of the slave flash unit, itproduces a voltage pulse which triggers the thyristor 3503 via theswitch 3501 and capacitor 3502, and thus the flash tube 3507 of theflash unit.

Thereafter, the light duration control device operates in the samemanner as it was described in connection with FIG. 6, i.e. the electriccurrent supply for the light receiver 3508 which now operates as aphotodiode, is supplied with an operating voltage and can no longeroperate as a remote triggering device as long as that current supply isnot interrupted, which does not occur until the end of the flash beingproduced by its flash unit.

On the other hand, when the switch 3501 is open, only the light durationcontrol function will be performed.

In case it is desired to produce an indirect flash, i.e. the flash unitis directed toward the ceiling or the wall, the light-sensitive elementof a known light duration control device would receive reflected lightform the ceiling or the wall, but not from the subject beingphotographed, so that the control device would not be responsive by theillumination of the subject being photographed.

To avoid these difficulties the present invention provides the use ofone or a plurality of light-sensitive elements whose position may beadjustable and which may be provided with light conductors, whichthemselves may also be adjustable. The setting of these elements mayoccur manually or automatically.

FIG. 27 shows an electronic flash unit incorporating such anarrangement. The unit is capable of being oriented to produce a directflash or a bounce flash. The light beam of the flash is directed andshaped in the usual manner by a lens 3604. The reflected light to bemeasured is received by an optical fiber element 3602 whose front faceis directed toward the source of reflected light to be measured andwhose rear face is di rected toward the light sensitive element 3601 ofa control circuit according to the invention. The front face of element3602 is aligned with a slot 3603 in the unit housing and is connected toany suitable mechanical arrangement (not shown) for undergoing a pivotalmovement to direct its front face toward the light to be measured. Fordirect flash, the element 3602 has the position indicated in solid linesand receives light coming in the direction of the solid arrow; forbounce flash where the unit radiates light at right angles to thesubject, unit 3602 has the position shown in broken lines and senseslight coming from the subject in the direction indicated by thebroken-line arrow. For intermediate bounce flash directions, unit 3602can be placed in any intermediate position between the two extremesillustrated.

In the case where the device contains a plurality of light-sensitiveelements which are oriented in different directions, the selection ofthe light-sensitive element or elements employed can be made byelectric, electronic, optical, or mechanical means, etc. The selectionmay be manual and/or automatic.

FIG. 28 shows a control circuit similar to those previously describedand employing a gas-filled switching tube 3701 which is provided with aninternal low voltage control or triggering electrode 3702.

The capacitor 3703 is connected to be charged by resistors 3704 and 3705to the voltage which is applied to the terminals of the gas-filledswitching tube 3701. When thyristor 3706 is fired, the voltage to whichcapacitor 3704 has been charged is applied to the internal low voltagecontrol electrode 3702 of the gas-filled switching tube 3701, so that itis also fired. The thyristor 3706 is connected in a circuit identicalwith that shown in FIG. 7.

FIG. 29 shows a circuit employing gas-filled switching tube 3808provided with an internal low voltage control electrode 3807 which iscontrolled by a low voltage pulse transformer 3809 which is in turndirectly controlled by a unijunction transistor 3606. Capacitor 3801,resistor 3802 and zener diode 3803 form an electronic current gate whichfunctions in the same manner as elements 309, 310 and 311 of FIG. 3.

The phototransistor 3804, the capacitor 3805 and the unijunctiontransistor 3806 form the integrator and threshold value detector, whichoperate in the same manner as the corresponding elements shown in FIG.7. The pulse generated by unijunction transistor 3806 is transmitted bythe pulse transformer 3809 to the internal low voltage control electrode3807 of the gasfilled switching tube 3808.

FIG. 30 shows a highly simplified control circuit including a gas-filledswitching tube 3902 provided with an internal low voltage controlelectrode 3903 directly controlled by the integration capacitor 3901.The terminal voltage of the integration capacitor 3901 controls thefiring of the gas-filled switching tube 3902 when a sufficient quantityof light has reached phototransistor 3904, directly through the internallow voltage control electrode 3903.

The circuit of FIG. 31 is substantially the same as that of FIG. 30except that the internal low voltage control electrode of the gas-filledswitching tube 4002 is controlled directly by a photoresistor 4001 whichsimultaneously serves as the light integrator. The control voltage ofthe internal electrode of the gas-filled switching tube 4002 is obtainedat the terminals of a variable resistor 4003.

FIG. 32 shows a circuit employing a gas-filled switching tube 4104provided with two internal low voltage control electrodes 4101 and 4102one of which is polarized by a voltage divider at a fixed voltagewhereas the other is controlled in the same manner as the controlelectrode of the circuit of FIG. 28. In the quiescent state, thevoltages at the two internal control electrodes 4101 and 4102 areidentical.

When the thyristor 4103 fires, there results an inequality between thesetwo voltages. This inequality has the effect of firing the gas-filledswitching tube 4104. Otherwise this circuit is the same as that of FIG.28.

The circuit of FIG. 33 employes a gas-filled tube 4203 without anyinternal or external control electrode. The firing of the tube iscontrolled by an electrically responsive light generating element, e.g.by a gallium arsenide diode. This apparatus operates in principle in thesame manner as the circuit shown in FIG. 29, except that the pulse ofthe unijunction transistor 4201 controls a light emitting diode 4202whose light pulse is directed toward the gas-filled switching tube 4203and initiates its firing.

In FIG. 34 there is shown one embodiment of the above-mentioned specialgas-filled tube of the arc arrester type. This consists of anelectrically isolating enclosure 2103, which can be transparent,translucent or opaque, whose interior 2105 is filled with a gas,preferably argon, and contains two preferably identical and unpolarizedelectrodes 2101 and 2102. A third firing electrode 2106 protrudes intothe interior 2105 of the enclosure 2103 and is extended by theconnecting wire 2107. The electrodes 2101 and 2102 are located andformed in such a way, and the filling and the pressure of the gas arechosen in such a manner, that this tube will function to perform an arcoperation.

As can be seen from FIG. 34a, which shows a modified embodiment of thedevice of FIG. 34, the enclosure 2103 is formed in the shape ofa tubeand is delimited by two electrodes 2101' and 2102' of the socket type,and of large surface area. The length of this tube is about the same asits diameter.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim: 1. A light sensing device for use in an automatic photoflashcomprising in combination:

a. light receiving lens means having two different angles of acceptance,the bisectors of which angles extend parallel to one another; and

b. light responsive means optically associated with said lens means forreceiving the light associated with both of said angles of acceptanceand producing an electrical output signal proportional to the timeintegral of the total received light.

2. An arrangement as defined in claim 1 further comprising optical fibermeans optically linked between said lens means and said light responsivemeans.

3. An arrangement as defined in claim 1 wherein said light responsivemeans includes a light-to-electric signal transducer, said arrangementfurther comprising an electronic computing circuit connected to receivethe output of said light responsive means.

4. An arrangement as defined in claim 3 wherein there are two suchtransducers having their electrical outputs connected together inparallel.

5. An arrangement as defined in claim 3 wherein there are two suchtransducers having their electrical outputs connected together inseries.

6. An arrangement as defined in claim 3 wherein there are two suchtransducers having their electrical outputs connected together in bothseries and parallel.

7. An arrangement as defined in claim 3 wherein said transducer is anintegrating device which produces an output signal proportional to thetime integral of the light which it receives.

8. An arrangement as defined in claim 3 wherein there are a plurality ofsuch transducers each producing an electrical output signal porportionalto the time integral of the light which it receives.

9. An arrangement as defined in claim 8 wherein said electroniccomputing circuit is connected to the output of each of saidtransducers.

10. An arrangement as defined in claim 9 wherein said computing circuitis constituted by a light duration control device for controlling theduration of the flashes produced by the photofiash in response to thelight received by said lens means.

1. A light sensing device for use in an automatic photoflash comprisingin combination: a. light receiving lens means having two differentangles of acceptance, the bisectors of which angles extend parallel toone another; and b. light responsive means optically associated withsaid lens means for receiving the light associated with both of saidangles of acceptance and producing an electrical output signalproportional to the time integral of the total received light.
 2. Anarrangement as defined in claim 1 further comprising optical fiber meansoptically linked between said lens means and said light responsivemeans.
 3. An arrangement as defined in claim 1 wherein said lightresponsive means includes a light-to-electric signal transducer, saidarrangement further comprising an electronic computing circuit connectedto receive the output of said light responsive means.
 4. An arrangementas defined in claim 3 wherein there are two such transducers havingtheir electrical outputs connected together in parallel.
 5. Anarrangement as defined in claim 3 wherein there are two such transducershaving their electrical outputs connected together in series.
 6. Anarrangement as defined in claim 3 wherein there are two such transducershaving their electrical outputs connected together in both series andparallel.
 7. An arrangement as defined in claim 3 wherein saidtransducer is an integrating device which produces an output signalproportional to the time integral of the light which it receives.
 8. Anarrangement as defined in claim 3 wherein there are a plurality of suchtransducers each producing an electrical output signal porportional tothe time integral of the light which it receives.
 9. An arrangement asdefined in claim 8 wherein said electronic computing circuit isconnected to the output of each of said transducers.
 10. An arrangementas defined in claim 9 wherein said computing circuit is constituted by alight duration control device for controlling the duration of thEflashes produced by the photoflash in response to the light received bysaid lens means.